Rectangle should be placed under radical
<math xmlns="http://www.w3.org/1998/Math/MathML" display="block"> <msqrt> <mtable frame="solid"> <mtr> <mtd> <mphantom> <mi>A</mi> </mphantom> </mtd> </mtr> <mtr> <mtd> <mphantom> <mi>A</mi> </mphantom> </mtd> </mtr> <mtr> <mtd> <mphantom> <mi>A</mi> </mphantom> </mtd> </mtr> </mtable> </msqrt> </math>